Effect of an epitaxial CoSi2 layer on diffusion of B and Sb in Si during annealing and oxidation

Abstract

The diffusion of B and Sb in Si, with and without a 20-nm-thick epitaxial CoSi2 layer on top, is investigated, during annealing and oxidation, using doping superlattices (DSLs). CoSi2 layers were grown on Si by molecular beam allotaxy. DSLs were grown by molecular beam epitaxy. They consisted of six spikes with peak concentrations of 1018 cm−3(B) and about 1019 cm−3(Sb) with peak centers spaced 100 nm apart. The shallowest spike was capped with 100 nm of Si followed by 20 nm of CoSi2. Annealing in pure N2 and oxidation in pure O2 were performed at temperatures ranging from 800 to 1200 °C. Concentration depth profiles were measured by secondary ion mass spectrometry. The results showed that the dopant diffusion in Si was markedly different with or without a CoSi2 layer. For specimens without CoSi2 layer, we observed oxidation enhanced diffusion of B and oxidation retarded diffusion of Sb in accordance with the literature. However, the effect of CoSi2 layer was a strong retardation of B diffusion and an enhancement of Sb diffusion. The B diffusivity was retarded by a factor of 2–10 as compared to the thermal diffusivity and by a factor of 20–100 as compared to the corresponding diffusivity for oxidation of Si without a CoSi2 layer. Sb diffusivity was enhanced by a factor of 2 with respect to thermal diffusivity and by about a factor of 5 as compared to the case without a CoSi2 layer.